Assignment of the Lowest Singlet and Triplet States of the Monoaldehyde of Durene

Abstract

The monoaldehyde of durene has been synthesized. It has been shown to be the impurity frequently encountered in spectral studies involving durene crystals. Both the polarized absorption and emission spectra of the protonated and deuterated aldehyde in crystals of durene^h-14 and durene^d-14 have been obtained. Although the lowest excited singlet and triplet states, separated by 2200 cm^?1, are shown to be nπ* a number of features in the phosphorescence spectrum are more characteristic of a ³π* state. The polarization of the absorption spectrum, in particular the 0-0 band and bands involving the excitation of totally symmetric vibrations, is inconsistent with the nπ* nature of the transition. A number of explanations is proposed.     

Phonon Side Bands of Specular Optical Transitions in Molecular Crystals

Quantitative investigations of phonon side bands (PSB) in the small radious centers absorption and luminescence spectra of some impurity molecular crystals are presented. Three pairs of specular spectra were considered corresponding to three impurity systems: benzene-d ⁰ in benzene-d ⁶, phenol in benzene-d ⁰ and β-methylnaphthalene-d ¹⁰ in naphthalene-d ⁸. Analysis of the observed spectra revealed such PSB regularities.

1) The most common characterization of PSB spectra is the deviation of the PSB shape from specular symmetry.

2) The non-specularness of the PSB shape does not depend on whether the PSB integral intensities are equal or different.

3) There is an unambiguous correlation between the expression of the PSB non-specularness and the temperature variation of the phononless band half width and shift.

4) For weak transitions, the non-specularness of the PSB integral intensities is observed in addition to the PSB shape non-specularness.

For the first time the observed characteristics were explained quantitatively in terms of the deviation from the Condon approximation on the basis of one-phonon spectra substracted from the PSB observed.     

Infrared Spectra and Photoinduced Absorption of C60 Doped Polyhexylthiophene

Abstract

We report the IR spectra and the photoinduced absorption of polyhexylthiophene(PHT) doped with C₆₀. The presence of C₆₀ ^?n anions is observed in the IR spectra by a mode at 1383 cm^?1 and a broad electronic transition at 1.2 eV, while most of the C₆₀ molecules stay neutral. This is indicative that for a small fraction of C₆₀ molecules, charge transfer occurs in the ground state.

The photoinduced absorption spectra display a sharp transition at 1.15 eV peculiar to C₆₀ monoanion, the spectral features change with fullerene concentration. The intensity of the polymer photoinduced bands increases 5-10 times due to photoinduced charge transfer to C₆₀.     

Optical Transitions of Agi and Agbr Clusters in Zeolite Fau

Abstract

AgI and AgBr clusters are both incorporated into the cages of zeolite FAU. The absorption spectra of these clusters, whose loading densities varied from dilute to four AgI and AgBr molecules per supercage, are discussed. In both samples, the lowest absorption band shifts to the lower energy side with increasing loading density. The large blue shift in AgI clusters compared to the bulk can be qualitatively explained by the model of strong quantum confinement of the photoexcited electron-hole pair. In the sample of AgBr clusters with four molecules per cage, however, the energy of the lowest absorption band is close to that of the lowest direct transition of AgBr in bulk. This apparently weak quantum confinement in the photo-excited state seems to originate from the singular band structure in the bulk, i.e., AgBr is the indirect gap material.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

Optical Properties of CuInSe2 Single Crystals Grown by the Vertical Bridgman Technique

The optical absorption near the fundamental edge of n-type CuInSe₂ single crystals was studied for samples having different impurity concentrations. It is found that with increasing impurity concentration the gap energy decreases whilst the tail absorption below the edge and its characteristic energy increase. It is concluded that band-gap narrowing due to high ionized impurity concentrations plays an important role in CuInSe₂ single crystals.     

Bulk and impurity infrared absorption in 0.5 As2Se30.5 GeSe2 glass

A study of infrared absorption in the 250–4000 cm^?1 region has been carried out for 0.5 As₂Se₃0.5 GeSe₂ glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm^?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As₂Se₃ and GeSe₂ glasses.Glasses doped with As₂O₃ exhibit the same oxide impurity absorptionbands as those doped with GeO₂. Unlike As₂Se₃ glass, at impurity concentrations up to 1000 ppm As₂O₃, 0.5 As₂Se₃0.5 GeSe₂ glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm^?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm^?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO₂ laser wavelength of 10.6 μm in both As₂Se₃ and 0.5 As₂Se₃ 0.5 GeSe₂ glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.     

Incorporation of H2 in vitreous silica, qualitative and quantitative determination from Raman and infrared spectroscopy

Incorporation mechanisms of H₂ in silica glass were studied with Raman and infrared (IR) microspectroscopy. Hydrogenated samples were prepared at temperatures between 800°C and 955°C at 2 kbar total pressure. Hydrogen fugacities (f_H2) were controlled using the double capsule technique with the iron–wüstite (IW) buffer assemblage generating f_H2 of 1290–1370 bars corresponding to H₂ partial pressures (P_H2) of 960–975 bars. We found that silica glass hydrogenated under such conditions contains molecular hydrogen (H₂) in addition to SiH and SiOH groups. H₂ molecules dissolved in the quenched glasses introduce a band at 4136 cm⁻¹ in the Raman spectra which in comparison to that of gaseous H₂ is wider and is shifted to lower frequency. IR spectra of hydrogenated samples contain a band at 4138 cm⁻¹ which we assign to the stretching vibration of H₂ molecules located in non-centrosymmetric sites. The Raman and IR spectra indicate that the dissolved H₂ molecules interact with the silicate network. We suggest that the H₂ band is the envelope of at least three components due to the occupation of at least three different interstitial sites by H₂ molecules. Both, Raman and IR spectra of hydrogenated glasses contain bands at 2255 cm⁻¹ which may be due to the vibration of SiH groups. Under the assumption that the reaction Si–O–Si + H₂ → Si–H + Si–O–H describes adequately the ‘chemical dissolution' of H₂ molecules, the SiH concentrations in our samples were determined and the molar extinction coefficient for the SiH absorption band in the infrared (₂₂₅₅(SiH)) could then be estimated to be 45 ± 3 l/mol cm. The solubility of molecular H₂ in our hydrogenated samples was determined using the IR absorption band at 4138 cm⁻¹ and the extinction coefficient given by Shelby [J. Non-Cryst. Solids 179 (1994) 138]. Samples quenched with different cooling rates gave nearly identical Raman and IR spectra, suggesting that the chemical dissolution of hydrogen (SiH and SiOH) can be quenched to room temperature without changing relative concentrations and that no exsolution of hydrogen occurred during the quench.     

An optical and structural investigation of rare-earth hydroxycarbonates

Physical data are given for the two polymorphs, ancylite type (A-type) and bastnaesite type (B-type), of the rare-earth hydroxycarbonates [Ln(OH)CO₃]. They include infrared absorption spectra and, in the case of neodymium electronic absorption spectra for the 4f ³ configuration recorded at 4 K.From the spectra one concludes that the rare-earth ion largely occupies a single site for both compounds. The OH infrared bands are very sharp. The optical data are compared with the results of structural investigations.     

First-principles calculations of the V3+ absorption spectra in LiAlO2 and LiGaO2

The systematic first-principles analysis of the energy level schemes and ground state absorption (GSA) of the V³⁺ ion in two oxide crystals LiAlO₂ and LiGaO₂ was performed. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron method (DV-ME) [K. Ogasawara, T. Iwata, Y. Koyama, T. Ishii, I. Tanaka, H. Adachi, Phys. Rev. B 64 (2001) 115413] was used in the calculations. The method is based on the numerical solution of the Dirac equation; no phenomenological parameters are used in the calculations. As a result, complete energy level schemes of V³⁺ ion and its absorption spectra in both crystals were calculated, assigned and compared with experimental data.     

Effects of Lattice Vacancy in Carbon Nanotubes Conductance Quantization

Abstract

Conductance of carbon nanotubes (CN's) with a lattice vacancy or strong and short-range impurity potential is studied within a tight-binding model. The conductance is quantized into zero, one, or two times the conductance quantum e ²/π? depending on the type of the vacancy if its size is much smaller than the circumference of CN.     

Effect of impurity adsorption on the growth of Rochelle salt crystals

The influence of impurities of copper compounds on the growth of Rochelle salt crystals of the composition KNaC₄H₄O₄ · 4H₂O is studied. The growth rates of the faces of various simple forms experimentally measured as functions of the CuCO₃ concentration in solution at a constant supersaturation and temperature are compared with the theoretical models of impurity adsorption on the faces of a growing crystal. Deceleration of the growth of various faces of a Rochelle salt crystal is satisfactorily described by the Bliznakov equation with the use of the Langmuir, Frumkin-Fowler, and de Boor adsorption isotherms for all the faces except for {010}. However, such a comparison does not allow one to reveal the cause of adsorption or its type on different faces. Photometric scanning of Rochelle salt solutions with copper-compound impurity showed that a small addition of alkali (0.06–0.4 g/l) to the solution results in the appearance in the absorption spectra of both the solution nd the crystal grown from it of a maximum at the wavelength 660–670 nm. The intensity of this maximum increases with an increase in the copper concentration. The EPR data, the absorption spectra of the solution and the crystal, and the modified crystal shape showed that the addition of alkali to the solution results in the formation of new copper complexes that more actively decelerate the growth of Rochelle salt faces.     

Near-edge Optical Properties of CuInSe2 Studied by Photoacoustic Spectroscopy

Optical absorption spectra of n-type CuInSe₂ single crystals were evaluated by means of photoacoustic spectroscopy in the photon energy range from 0.94 to 1.02 eV. At photon energies below 0.99 eV the spectra exhibit exponential tails that are ascribed to the presence of shallow impurity states. At higher photon energies the absorption coefficients follow the relation for direct allowed optical transitions between parabolic bands. The parameters of this relation are determined and compared with previous measurements.     

Supramolecular Architecture of Two Modifications of Flavone-6,2′-dicarboxylic acid

Abstract  

Two crystalline forms of flavone-6,2′-dicarboxylic acid (fla): one N,N-dimethylformamide (DMF) solvate (modification 1) and one without any solvate molecules (modification 2), have been obtained and their structures were determined by X-ray diffraction technique. Modification 1 crystallized in the orthorhombic space group Pbca; and modification 2 crystallized in the monoclinic space group P2(1)/c. In 1 and 2 fla molecules are both joined to helix chain structures via O–H···O hydrogen-bonds between carboxylic group of B ring and carbonyl oxygen atom of C ring, however, in 1 helix chains are further joined by DMF molecules; and in 2 helix chains are further linked via rich hydrogen-bonds between fla molecules, which result in different packing of modifications 1 and 2.     

Induction of B1, B6 and Biaxial Smectic A Phases in Binary Mixtures of Compounds with Rod-Like and Bent-Core Molecules

Abstract

We have studied a binary mixture of compounds, one of which has rod-like molecules and the other bent-core molecules. The rod-like molecules are biphilic in nature with a long alkoxy chain attached to an aromatic moeity only at one end, and exhibit the bilayer SmA₂ phase, even though they do not have the highly polar cyano or nitro groups. The compound with bent-core molecules exhibit the B₂ phase which has polarized layers with tilted molecules. Three liquid crystalline phases are induced in the binary mixtures, depending on the concentration: the 2-dimensionally ordered B₁ phase for compositions with 15 to 63 mol% of the rod-like molecules and the B₆ phase for 63 to 87 mol%. The sequence obtained on increasing the concentration of rod-like molecules is the same as that seen on shortening the chain length of the BC molecules. Between 87 to 95.5 mol% of the rod-like molecules, a new biaxial smectic A₂ (SmA_2b ) phase is induced. On the basis of several observations, we argue that it corresponds to a structure in which the BC molecules are reoriented with their arrow directions pointed along the layer normal. The SmA₂ to SmA_2b transition corresponds to an orientational transition of the bent-core molecules in the anisotropic SmA₂ background medium.     

Molecular Organization of Porphyrin-Metal Complexes

Abstract

Tetraethyltetramethylporphyrin substituted at two facing meso positions by N-methylimidazolyl groupings and its metal complexes were prepared. The absorption spectra of Zn and Mg complexes showed a characteristic splitting of Soret band and red-shifts of Q-bands indicating the exciton interaction of porphyrins in a slipped cofacial arrangement, where each imidazolyl group in one metal porphyrin is coordinated to metals in the other porphyrin skeleton. Typical upfield shifts in the ¹H NMR spectra arising from such the stacking structure elucidated Zn and Mg complexes as a dimer and an oligomeric mixture, respectively. Bis(imidazolyl)substituted tetraethyltetramethyl-porphyrin was also prepared. It suggested the hydrogen bonded oligomer formation through imidazolyl-imidazolyl interactions in a columnar orientation.

Electric conductivities of films prepared from these compounds werecharacterized. In a same line with behaviors in solution, samples capable of π-stacking interaction with adjacent porphyrins via ligand-to-metal coordination or hydrogen bonding exhibited higher conductivities as well as lower activation energies for the thermal conduction. These behaviors are understood as due to the overlap of π-systems of one porphyrin with neighboring porphyrins.     

The effect of solvent polarity on second order hyperpolarizability of selected phthalocyanines complexes

ABSTRACT

The effect of the solvent polarity on nonlinear optical properties of selected phthalocyanines complexes of copper, cobalt, zinc and magnesium using degenerate four wave mixing (DFWM) method is presented. Ethanol and dimethyl sulfoxide were used as solvents for all studied complexes. The solvent effect is observed for the absorption spectra of metal phthalocyanines (MPcs) solutions. It was noticed that the solvent polarity as well as the central metal ion play a crucial role in determining the values of the second order hyperpolarizability (γ_eff) of studied macrocyclic compounds. In general, γ_eff values of MPcs solutions are changing with change of the solvent polarity in order of ZnPc > MgPc > CuPc > CoPc. And these values are higher for samples dissolved in polar aprotic solvent than in polar protic solvent.     

A novel stable CuI complex based on an unconjugated bisanthryl-tethered diimine ligand with tri-coordinate mode

The first air-stable mononuclear Cu^I complex (1) based on an unconjugated bisanthryl-tethered diimine ligand has been synthesized and characterized by elemental analysis, ESI-MS, UV-vis, FT-IR spectra and TGA analysis. X-ray diffraction analysis at room temperature reveals that complex 1 crystallizes in a monoclinic system, space group P2₁/c with a=15.611(3) ?, b=24.412 (5) ?, c=15.430 (6) ?, β=114.49 (3)°, V=5351.3 (19) ?³, ρ _calc=1.359 g cm⁻³, μ=0.472 mm⁻¹ and Z=4. The crystal structure of 1 features a mononuclear tricoordinated complex with a distorted triagonal planar geometry. The Cu^I center is coordinated to three imine N atoms of two Schiff base ligands, while the remaining one imine N atom keeps uncoordinated. UV-vis absorption and emission spectra indicate that the complexation of metal ion has slight influence on the electronic structure of the ligand. TGA analysis confirms that complex 1 is stable up to 253°C.Supplementary materials Crystallographic data reported in this paper have been deposited with Cambridge Crystallographic Data center (CCDC no.282672). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc. cam. ac.uk).